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This paper presents a novel cryogenic cooling method for Superconducting Radio Frequency (SRF) cavities, utilizing a cold helium flow passed through a brazed capillary for their cooling. Such novel and drastically reduced helium content cooling scheme can be applied to a wide variety of superconducting cavities, and it has many advantages compared to the traditional cooling method of SRF cavities in a liquid helium bath. The paper describes cooling options and configurations concerning helium forced flow heat transfer at the capillary surface plus the conduction pathway and the resulting temperature distribution in the cavity itself. A detailed description is provided for the proof-of-concept cryogenic performance test stand, which studies the relevant parameters for a 1.3 GHz prototype cavity.
The results of the numerical evaluation of heat transfer and pressure drop relations for two-phase and single-phase supercritical flow, as well as the results of the mechanical vibration measurements, are cited. Moreover, the results from the cold commissioning of the experimental system are outlined, demonstrating that the cavity could reach a minimum temperature of 6.5 K with an applied heat load of 1 W, with a He circulation loop based on a 1.8 W @ 4.2 K cryocooler. A LHe booster heat exchanger has been introduced to achieve even lower temperatures and ensure consistent inlet conditions for further evaluation of cavity cooling efficiency. These data form the basis for future experimental validation campaigns in the temperature range of 4.2 K to 10 K and helium pressures of up to 2.2 MPa. Special attention is paid to possible new introduced effects of mechanical vibrations or temperature gradients along the cooling capillary when compared to a stagnant He bath cooling.
Keywords — Dry cavity cooling, superconducting radiofrequency (SRF) cavities, low temperature, helium capillary cooling
| Submitters Country | Switzerland |
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